This invention relates to transmitters and transmitting methods, and more particularly to transmitters and transmitting methods that can transmit multiple radio frequencies.
Transmitters are widely used to transmit radio frequency communications. In particular, in radiotelephone base stations, a transmitter generally transmits a plurality of radio frequencies from a common antenna. At each radio frequency, a radio channel frequency signal that is modulated with information modulation is transmitted.
Unfortunately, it may be difficult to couple a plurality of a radio channel frequency signals to a common antenna without appreciable loss. In particular, the radio channel frequency signals generally are amplified by a respective plurality of power amplifiers, and it may be difficult to couple the outputs of the power amplifiers to a common antenna without appreciable loss. Frequency selective combiners previously have been used to couple adjacent channel amplifiers to the common antenna. Unfortunately, these combiners may waste significant energy as heat, and/or may not be selective enough to allow adjacent channels to be combined unless they use cooled, superconductive resonators.